Make sure your sweep volumes are all roughly the same level. Best to do this through the "secret menu", playing pink noise through each channel, and measuring with an iPhone app. Since you cannot use the LP trick to chop off frequencies above 200Hz from the underseats (MS-8 "design" flaw), you have to artificially lower the output of the underseats by around 4-6dB compared to the other channels. The reason for this is a bit complicated to explain but if you want to know, read this thread: http://www.e90post.com/forums/showthread.php?t=724447